Detection Methods for Shiga Toxins and Shiga Toxin-Producing E. coli

Shiga toxin detection methods reflect the complicated biological processes that deliver these toxins to their target cells. Some detection methods employ techniques that indirectly detect the presence of Shiga toxins. Microbiological methods are used to identify pathogenic serotypes of E. coli, such as the infamous O157:H7, but the potential production of Shiga toxins is uncertain and depends on the strain. Similarly, PCR methods detect the presence of genes that code for Stx and pathogenicity factors, from which the potential presence of Stx is inferred. Bioassays detect Shiga toxins by the biological responses of cells, tissues, or animals. The ability of some antibodies to inhibit toxin activity has been exploited to make in vitro activity tests toxin-specific. Structural assays detect a 3-dimensional shape (immunoassay) or the masses of peptides that are liberated from toxin subunit chains by a protease (mass spectrometry). Many immunoassay systems have been able to detect and distinguish among Shiga toxin types, subtypes, and variants. Some antibodies have helped to elucidate toxin mechanisms and could be the basis of toxin therapeutics. Mass spectrometry has been used for direct detection of Stx and to distinguish among the Stx types and subtypes. The Multiple Reaction Monitoring (MRM) method is reviewed in depth.